Blood glucose + Water

AQA A-Level Biology Topic 6

What is glucose used for in mammals?

a substrate for respiration

a main source of providing energy

Why is it essential for mammals to maintain a constant concentration of glucose?

Glucose is the main energy source required for respiration

What will happen in glucose concentration falls too low in mammals?

Cells will be deprived of energy and die

What will happen in glucose concentration reaches too high in mammals?

it lowers the water potential of the blood and creates osmotic problems that can cause dehydration

What is the function of the pancreas?

Produces enzymes for digestion

Produces hormones for blood glucose regulation

Name 3 enzymes that the pancreas produces for digestion.

protease

amylase

lipase

Name the 2 hormones that the pancreas secretes for regulating blood glucose concentration.

insulin

glucagon

What is the pancreas mostly made up of?

the cells that produce its digestive enzymes

What is distributed throughout the pancreas between the cells that produce its digestive enzymes

Islets of Langerhans

What are Islets of Langerhans

Groups of hormone producing cells located in the pancreas

What 2 types of cells are included in the Islets of Langerhans?

Alpha cells

Beta cells

What do Alpha cells in the Islets of Langerhans produce?

glucagon

What do Beta cells in the Islets of Langerhans produce?

insulin

What is the normal blood glucose concentration?

5 mmoldm-3.

What are the three sources that blood glucose comes from?

From the diet

From hydrolysis of glycogen

From gluconeogenesis

Describe how blood glucose comes from the diet.

Directly from the diet in the form of glucose absorbed following hydrolysis of other carbohydrates

Describe how blood glucose comes from hydrolysis of glycogen

Hydroylsis in the small intestine of glycogen stored in the liver and muscle cells

Describe how blood glucose comes from gluconeogenesis

the production of glucose from sources other than carbohydrates

Describe how blood glucose can fluctuate in animals.

Blood glucose increases after eating foods containing carbohydrates and

decreases when not eating and after exercise as glucose is used in respiration to release energy

What are the cells that make up the liver called?

hepatocytes

Where do the hormones insulin and glucagon take their effects?

The liver

Name the 3 processes associated with regulating blood sugar that take place in the liver.

Glycogenesis

Glycogenolysis

Gluconeogenesis

What is glycogenesis?

The conversion of glucose into glycogen

Describe the process of glycogenesis.

When blood glucose concentration is higher than normal the liver removes glucose from the blood and converts it to glycogen.

How much glycogen can the liver store?

75-100g

How long can 75-100g of glycogen maintain a humans blood glucose concentration for?

12 hours

What is glycogenolysis?

The breakdown of glycogen into glucose

Describe the process of glycogenolysis.

When blood glucose concentration is lower than normal, the liver can convert stored glycogen back into glucose

Glucose diffuses into the blood to restore the normal blood glucose concentration.

What is gluconeogenesis?

the production of glucose from sources other than carbohydrate

Describe the process of gluconeogenesis.

When its supply of glycogen is exhausted, the liver can produce glucose from noncarbohydrate sources such as glycerol and amino acids.

Describe the action of the Beta cells in the Islets of Langerhans.

The beta-cells of the islets of Langerhans in the pancreas have receptors that detect the stimulus of a rise in blood glucose concentration and respond by secreting the hormone insulin directly into the blood plasma.

What secretes the hormone insulin into the blood plasma?

Pancreas / beta cells in islets of langerhans

Describe the action of insulin in controlling blood glucose concentration.

1. Insulin attaches to specific receptors on the CSM of liver and muscle cells, causing a change in tertiary structure of the glucose transport carrier proteins, causing them to change shape and open, allowing more glucose into the cells by facilitated diffusion. The cell membrane is more permeable to glucose.

2. When insulin binds to receptors on the CSM it triggers the movement of vesicles containing GLUT4 to the membrane where it fuses, and increases the number of glucose transport channels. Glucose is transported into the cell through GLUT4 by facilitated diffusion from blood.

3. Insulin activates enzymes involved in glucogenesis.

Activating enzymes involved in the conversion of glucose to glycogen in liver and muscle cells (glycogenesis) The cells are able to store glycogen in their cytoplasm as an energy source.

Increasing the rate of respiration of cells This therefore uses up more glucose, thus increasing their uptake of glucose from the blood

What is GLUT4

a glucose transporter channel protein which is stored in vesicles when insulin is low.

What does glucagon do?

Raises blood glucose concentration

Describe how alpha cells in the islets of langerhans detect and respond to a change in blood glucose concentration.

They have receptors that detect the stimulus of a drop in blood glucose concentration, then respond by secreting glucagon into the blood plasma.

Describe the 4 ways in which glucagon increases blood glucose.

1. Attaches to specific receptors on the cell surface membranes of liver cells, the target cells.

2. Activating enzymes involved in the conversion of glycogen to glucose in liver cells (glycogenolysis)

3. Activating enzymes involved in the conversion of glycerol and amino acids into glucose (gluconeogenesis)

4. Decreases the rate of respiration in cells. So less glucose is being broken down to release energy so there are greater concentrations in the blood.

Does adrenaline raise or lower blood glucose concentration?

Raises

What is adrenaline

a hormone secreted from the adrenal glands

Where is adrenaline secreted from?

adrenal glands

When is adrenaline secreted?

When there is a low concentration of blood glucose when excited, stressed or exercising

Describe the 3 ways in which Adrenaline increases blood glucose.

1. Attaches to specific receptors on the cell surface membrane of liver cells. This causes a G protein to be activated and convert ATP into cAMP, which activates an enzyme hydrolyses glycogen into glucose, therefore activating glucogenolysis.

2. Inhibits glycogenesis, preventing the synthesis of glycogen from glucose

3. Activates glucagon secretion and inhibits insulin secretion

What is diabetes?

A disease where blood glucose concentration cannot be controlled naturally due to the lack of insulin or the loss of a responsiveness to insulin.

Describe what Type 1 Diabetes is.

A disease where the body is unable to produce its own insulin, since the immune system attacks the beta-cells on the islets of Langerhans so they cannot produce any insulin. After eating, blood glucose concentration stays high (hyperglycaemia). The kidneys cannot reabsorb all the glucose, so some is excreted in urine.

What is the cause of type 1 diabetes?

The result of an autoimmune response where the body attacks self beta-cells

When does type 1 diabetes usually develop?

in childhood

What could make somebody be more at risk for type 1 diabetes?

Having a genetic predisposition

Describe how type 1 diabetes can be controlled through insulin.

Through insulin therapy: injecting insulin throughout the day or using an insulin pump

Why does insulin therapy need to be monitored carefully?

Too much insulin can cause dangerous drop in blood glucose (hypoglycemia)

How can the correct dose be ensured during insulin therapy?

by monitoring blood glucose concentration through biosensors

Describe how Type 1 diabetes can be controlled through diet.

Eating regularly and controlling simple carbohydrate intake helps to avoid sudden rises in glucose. 

Describe what is meant by type 2 diabetes.

Beta cells do not produce enough insulin or when the body cells do not respond properly due to receptors on the target cells losing their responsiveness to insulin.

Describe the causes / aquisition of Type 2 diabetes.

Usually acquired later in life

Linked with obesity, lack of exercise and poor diet

It is more likely in people with a family history of type II diabetes.

It develops slowly, and the symptoms are normally less severe and may go unnoticed.

Describe how Type 2 diabetes can be controlled through Insulin.

Injections of insulin or use of drugs that stimulate insulin production

Other drugs can slow down the rate at which the body absorbs glucose from the intestine and stimulate kidneys to make you wee out extra sugar.

Describe how Type 2 diabetes can be controlled through diet.

Treated by eating a healthy, balanced diet, losing weight and exercising regularly.

Reduced sugar intake in diet and eating food with low glycaemic index so there is less sugar absorbed into blood

Reduced fat intake so less fat converted to glucose

More regular exercise so uses glucose by increasing respiration

Lose weight so increased sensitivity of cells to insulin

Evaluate the positions of health advisers and the food industry in relation to the increased incidence of type II diabetes

Type 2 diabetes is becoming increasingly common in the UK and can cause additional health problems such as kidney failure.

Health advisers should recommend people to consume a diet low in fat, sugar and salt with plenty of whole grains, fruit and vegetables.

The food industry should tackle the problem by reducing the advertisement of junk food to children, and using sweetner alternatives.

However, companies want to increase profits.